Wire and cable coverings, sheathes, jackets, and films exhibiting desirable flame retardant performance are sought in the industry. Customers often require or demand compositions meet minimum standards such as the Underwriters' Laboratory (UL) 94 VB Test, with a VO rating at a specified thickness. In addition, film or wire and cable producers require extrudable compositions for some applications. Most styrenic block copolymer-based thermoplastic elastomer (TPE) compositions require the use of a mineral oil as a plasticizing softener. Without the plasticizing softener, the flame retardant containing TPE compositions can be difficult to process and extrude. However, the use of a softener can significantly reduce the flame retardant performance of such compositions.
U.S. Patent Application publication 2013/0065051 A1 relates to halogen-free, flame-retardant thermoplastic compositions that include a styrenic block copolymer, a low-melting, phosphorus-based flame retardant having a melting temperature no higher than 170° C., and a blend of solid intumescent phosphorus and nitrogen-containing flame retardants. The blend of solid intumescent flame retardants include at least two phosphorous and nitrogen-containing phosphoric acid salts that reportedly synergistically enhance the flame-retardant properties of the compositions relative to compositions that include other flame-retardant packages.
U.S. Patent Application publication 2012/0261163 A1 disclose a halogen-free, flame retardant thermoplastic resin composition based on polypropylene and one or more thermoplastic elastomers with an organic nitrogen- and/or phosphorus-based intumescent flame retardant comprising a piperazine component. The composition is processed easily to make a wire and cable sheath reportedly exhibiting a balance of high flame retardancy, good flexibility, high wet electrical resistance and excellent heat deformation properties, and which reportedly passes the VW-I flame retardancy test, the US1581 heat deformation test at 150° C., and the wet electrical resistance test, and also exhibits good tensile and flexibility properties. Also disclosed is a wire and cable sheath made from the composition.
In view of the above, one problem of the present invention was to provide extrudable thermoplastic elastomer compositions that are halogen-free and exhibit excellent flexibility and flame retardant performance. Still another problem of the present invention was to provide thermoplastic elastomers having low or no mineral oil softener content, yet remain easily processable and extrudable.
Another problem of the present invention was that mineral oils typically utilized to make styrenic block copolymer-based halogen free flame retardant thermoplastic elastomers processable can significantly reduce the flame retardancy performance. Simply replacing the mineral oil with a liquid flame retardant can cause the liquid flame retardant to leach out of the processed, e.g. molded or extruded, composition leading to surface tackiness. The use of a relatively low styrene content styrenic block copolymer allows the use of softener free compositions, although flexibility and physical strength of the thermoplastic elastomer can be poor.